complete information regarding gene action in plants

1. Gene action in plants
Submitted to
Dr. M. A. Hanumant
Deptt. Of Genetics and
Plant Breeding
submitted by
Chanda kumari
Ph.D scholar
Deptt. Of Genetics and Plant
Breeding
Assignment on

2. Introduction
Genes are the functional units that govern the development of various characters
of an individual.
Gene Action refer to the behavior or mode of expression of genes in a genetic
populations.
Genes control synthesis of proteins which in turn control expression of various
traits of an organism.
Gene action was first studied by Archibald Edward Garrod (1902) for metabolic
disorder in men further in Drosophilla, neurospora and bacteria.
Knowledge of gene action helps in the selection of parents for use in
hybridization programmes and also in the choice of appropriate breeding
procedure for the genetic improvement of various quantitative characters.
Klence insight into the nature of gene action involved in the expression of
various quantitative characters is essential to a plant breeder for starting a
judicious breeding programme.

3. • When expression of one gene depends on the presence or
absence of another gene in an individual, It is known as
gene intraction.
• Gene interactions occur when two or more different
genes influence the outcome of a single trait .
• Interaction between allelic or nonallelic genes of the
same genotype in the production of particular phenotypic
characters .
GENE INTRACTION

4. Salient Features of Gene Action
1. Gene Action is measured in term of components of genetics variance or
combining ability variance and effects .
2. Depending upon the genetic variance , gene action is of three type , viz. additive
gene action, dominance gene action and the epistatic gene action. Dominance
and epistatic gene action jointly are referred to as non-additive gene action.
3. Gene Action can be studied with the help of various biometrical techniques such
as diallel analysis, partial diallel cross .triallel analysis, quadriallel analysis line
X tester analysis generation biparental cross and triple test cross analysis
4. Gene Action is affected by various factors.

5. Cont…
Gene action is of two types:
1. Additive gene action (fixable variation)
2. Non-additive gene action (Un fixable variation)
Additive gene action includes additive genetic variance and additive x additive type of epistatic
variance.
Non additive gene action includes :1. Dominance variance (d) or D
2. Epistatic variance
Additive x additive variance (i) or I Additive x
dominance (j) or J
Dominance x dominance (l) or L

6. Types of gene action
.
Gene action
Allelic
Non allelic
1. Complete dominance
2. Incomplete dominance
3. Co-dominance
1. Supplementary gene action
2. Complementary gene action
3. Lethal gene action
4. Inhibitory gene action
5. epistatic gene action
6. Pleiotropic gene action
Additive
Non additive

7. Gene Action and Plant Breeding
The science of plant genetics trace back to Mendel’s classic studies with garden
peas.
Mendel’s evaluated crosses of pure lines and by scoring phenotypes he deduced
the existence of genes and determined their mode of action.
Plant breeder identify superior genotype and develop new cultivars by
selecting plants possessing desirable phenotype derived from genetic
recombination. The understanding of gene action isof paramount importance to
plant breeders.
Knowledge of the way gene act and interact will determine which breeding
system optimizes gene action more effectively and will elucidate the role of the
breeding systems in the evolution of crop plants.

8. NON ADDITIVE GENE ACTION
Non additive gene action: one allele is expressed stronger
than the other allele.
a) Allelic/Dominance - in which the effect on phenotype of one
allele masks the contribution of a second allele at the same
locus. This type of interaction gives the classical ratio of 3:1
or 9:3:3:1. it is of three types – incomplete, complete,
overdominanc.
b) Non-allelic/ epistatic gene interaction - the interaction of
genes at different loci that affect the same character called
epistasis.

9. Dominance Action (D)
 It refers to the deviation from the additive scheme of gene action resulting from intra-allelic
interaction.
 It is due to the deviation of heterozygote (Aa) from the average of two homozygotes (AA and aa).
 When d = (Aa-m) 0, gene A is showing dominance action.
 Depending upon the position of heterozygote in relation to m on the hereditary scale : Complete,
Partial, Over-dominance.

10. Complete dominance is a form of dominance in heterozygous
condition wherein the allele that is regarded as dominant
completely masks the effect of the allele that is recessive.
Complete Dominance

11. Mirabilis Jalapa (4 O’clock plant)
INCOMPLETE DOMINANCE
 Incomplete dominance (partial dominance) where
dominance of an allele over other is not complete .
 Third phenotype appear which are differ from parent
homozygote phenotype but are closer to one
homozygous phenotype than the other.
 Ratio- 1:2:1
 Example:

12. OVER DOMINANCE
 Over Dominance is the interaction between genes that are alleles
and result in the heterozygous individuals being superior to
either of their homozygotes.
OR
 Overdominance can also be described as heterozygote
advantage, wherein heterozygous individuals have a higher
fitness than homozygous individuals.
 Ex: A particular blood type in rabbits.
sickle cell anemia

13. CODOMINANCE
 Codominance is a form of dominance wherein the alleles of a gene pair in
a heterozygote are fully expressed. This results in offspring with a
phenotype that is neither dominant nor recessive.
 Codominance is most clearly identified when the protein products of both
alleles are detectable in heterozygous organisms .
 Example: AB Blood group. a person having A allele and B allele will have a
blood type AB because both the A and B alleles are codominant with each
other.

14. EPISTASIS
 when two different genes which are not alleles, both affect
the same character in such a way that the expression of one
masks, inhibits or suppresses the expression of the other
gene, it is called epistasis.
 Gene that masks = epistatic gene
 Gene that is masked = hypostatic gene

15. Epistatic (inter-allelic interaction) (I)
It refers to the deviation from additive scheme as a consequence of
inter-allelic interaction, i.e., interaction between alleles of two or
more different genes or loci.
Main features:
Epistatic variance includes both additive and non-additive
components.
It is of three types : Additive x Additive
Additive x Dominance
Dominance x Dominance
First type of epistasis is fixable and therefore, selection is effective
for traits governed by such variance.

16.  Last two type of epistatic variances are unfixable – heterosis
breeding may be rewarding.
 In case of generation mean analysis, the epistatic gene
interactions are classified on the basis of sign (negative or
positive) of (h) and (l) into 2 types: complementary
duplicate
• When (h) and (l) have the same sign, it is called complementary
type.
• When (h) and (l) have opposite sign, it is termed as duplicated
tpe of epistasis.
 In the natural plant breeding population, epistatic variance has
the lowest magnitude.

17. Classification of epistatic gene interaction
• Epistatic gene interaction Gene is classified as follow on
the basis manner by which concerned genes influence
the expression of each other
1. Supplementary gene action (9:3:4)
2. Complementary gene action (9:7)
3. Inhibitory gene action (13:3)
4. Duplicate gene interaction (15:1)
5. Masking gene action (12:3:1)
6. Polymeric gene action (9:6:1)

18. 1. Supplementary gene action (9:3:4)
• When recessive alleles at one locus mask the expression of
both (dominant and recessive) alleles at another locus.
• However dominant allele of the other gene does not produce
a phenotypic effect on its own.
Ex: development of agouty (gray) coat color in mice.
grain colour in maize.

19. GRAIN COLOUR IN
MAIZE(Purple, red &
white)
Purple- presence of 2 dominant
genes (R & P)
Red- dominant gene R
White- homozygous recessive
condition
r is recessive to R, but epistatic to
alleles P & p.

20. 2. Complementary gene interaction 9:7
• When recessive alleles at either of the two loci can mask the expression
of dominant alleles at the two loci, it is called duplicate recessive
epistasis.
• In such case, the genotype aaBB, aaBb, Aabb, aabb produce
one phenotype.
called
• Both dominant alleles when present together each other are
complementary genes and produce a different phenotype.
• Ex: Flower colour in sweet pea.

21. Here recessive allele c is epistatic to P/p alleles & mask the expression of these alleles. Another
recessive allele p is epistatic to C/c & mask the expression of these alleles. Hence in F2, plants with C-
P- (9/16) = Purple flower and plants with genotype ccP- (3/16), C-pp-(3/16) & ccpp (1/16)
producewhite flowers.
Flower colour in sweet pea
Purple-9: white-7.

22. 3. Inhibitory gene action (13:3)
• When dominant allele of one gene locus (B) in homozygous
(BB) and heterozygous (Bb) condition produce the same
phenotype the F2 ratio becomes 13:3 instead of9:3:3:1
• While homozygous recessive (bb) condition produces different
phenotype.
• Homozygous recessive (bb) condition inhibits phenotypic
expression of other genes so know as inhibitory geneaction

23. Ex: Anthocyanin pigmentation in rice
The green colour of plants is governed
the gene I which is dominant over
purple colour.

24. 4. Duplicate gene interaction(15:1)
• When dominant allele of both gene loci produce
the same phenotype without cumulative effect
• In that case the ratio becomes 15:1 instead of
9:3:3:1
• Occurs in shepherds purse plant and awn
character in rice.

25.  In shepherds purse plant seed capsule occurs in two
shapes i.e. triangularand ovoid shapes.
 Ovoid shape seed capsule occurs when both genes
are present in homozygous recessive condition

26. 5. Masking gene action/dominant epistasis (12:3:1)
• When out of two genes, the dominant allele (e.g., A) of one
gene masked the activity of both allele (dominant or recessive)
of another locus.
• Then A gene locus is said to be epistatic to the B gene locus.
• Dominant allele A express itself only in the presence of either B
or b so such type of epistatic is know as dominant epistatic.
• The allele of hypostatic locus express only when the allele of
epistatic locus present in homozygous recessive condition.

27. FRUIT COLOUR IN SUMMER SQUASH
• Three colours: white, yellow & green.
• White colour is controlled by dominant gene W and yellow
colour by dominant gene G.
• White is dominant over bot yellow and green.
• Green colour fruits are produced in recessive conditions
(wwgg).

28. Polymeric gene action 9:6:1
Two dominant alleles have similar effect when they are separate,
but produce enhanced effect when they come together
Example: squash fruit shape
Plant at least one dominant at each locus (A-b-)
have disc shaped fruit. plant with recessive allele
at each locus (aabb) produces long fruit and plant
are homozygous recessive at either of the loci (A-
bb or aaB- ) produce spherical fruit .

29. Breeding procedure to be followed
 Heterosis breeding
 Population improvement by recurrent selection for sca

30. Steps involve in gene action
1. Selection of genotypes.
2. Making crosses.
3. Evaluation of material.
4. Analysis of data.

31. 1. Selection of genotypes: include varieties, strains or germplasm lines.
2. Making crosses: The selected genotypes are crossed according to the
mating design to be used.
Choice of mating design depends on the type of genetic material. The
mating designs, diallel, partial diallel, and line x tester analysis are
commonly used for estimation of genetic variances from single crosses.
• Triallel analysis : used for estimation of genetic variances in three-
way crosses.
• quadriallel analysis : evaluation of double crosses.
• Triple test cross analysis provides information about the presence or
absence of epistasis in addition to the estimates of additive and
dominant components.
• Three biometrical techniques ,viz., generation mean analysis, triallel
analysis and quadriallel analysis provide information about all the
three components of genetic variance, viz., additive, dominance and
epistatic variances.

32. 3.) Evaluation of material:
The crosses made among selected genotypes are
evaluated along with parents in replicated trials and
observations are recorded on various quantitative
characters.
4) Analysis of Data:
The biometrical analysis of data is carried out as per
the mating design adopted. Diallel , partial diallel,
line x tester analysis and biparental cross analysis
provide estimates of additive and dominance
components of genetic variance.

34. Factor affecting gene action
1. Type of Genetic Material:
The magnitude of gene action is largely governed by the type of genetic material
used for study.
 In a F2 or advanced generation : the genetic variance includes additive,
dominance, and epistatic components.
 Homozygous lines : the genetic material is entirely of additive and additive –
epistatic types.
2) Mode of pollination:
The gene action is greatly influenced by the mode of pollination of a plant species.
 Self pollinated species : additive gene action is associated with homozygosity.
Inbreeding increase the amount of additive genetic variance in a population due to
increase , in homozygosity by way of gene fixation.
 Cross-pollinating crops : Dominance gene action is associated with heterozygosity.

35. Genetic material
(a) Self pollinated species
Pure lines variety
Mass selected variety
Multilines
Varietal blend
(b) Cross pollinated species
Composite variety
Synthetic variety
Random mating population
(c) Both self and cross
pollinated
species
F1 Hybrid
F2 Population
Types of geneAction
Additive but no genetic variation
Additive and additive epistasis
Additive and additive epistasis
Additive and additive epistasis
Additive , dominance and epistasis
Additive, dominance and epistasis
Additive ,dominance and epistasis
Non-additive and no genetic variation
Additive ,dominance and epistasis
Type of Genetic material

36. 3)Mode of Inheritance:
Polygenic characters are governed by both additive and non- additive type gene action , though the additive gene action is
predominant in the expression of such characters.
On the other hand, oligogenic traits are primarily governed by non additive type of gene action.
In case of oligogenic trait, epistasis variance is of widespread occurrence, but comparable evidence for polygenic trait is
meagre(Frey,1966).
4) Sample size:
The estimates of genetic variance are influenced by the sample size on which the computation is based. Sample size should
be adequate to obtain consistent and meaningful results. Small sample may not provide estimates of sufficient reliability.
5). Existence of linkage
The existence of linkage also affects the gene action.
Linkage influences gene action by causing an upward or downward bias in the estimates of additive and dominance genetic
variances.
There are two phases of linkage , viz coupling and repulsion. In case of coupling phase , there I linkage either between
dominant gene (AB)or between recessive genes(ab).
The repulsion phase refers to linkage between dominant and recessive genes (Ab/aB)

37. Effect of linkage on gene variance:
:
Downward bias in
Type of linkage Upward bias in
Coupling
phase
(AB/ab)
Repulsion
phase
Additive variance
Dominance
variance
Dominance
variance Additive variance
-

38. Cont…
High frequency of coupling phase (AB/ab) cause an upward bias in the
estimates of Additive and dominance variance (Hallauer and Miranda,
1981).An excess of repulsion phase linkage (Ab/aB) leads to upward
bias in dominance variance and downward bias in the additive variance
Linkage disequilibrium can be reduce by random mating of population. In
other word s. linkage can be broken by repeated intermating of randomly
selected plants in segregation populations.
The number of intermating generations required for breaking the
depends on the closeness of the linkage

39. Case study
Gene action of fruit yield and quality traits in okra (Abelmoschus esculentus (L.) Moench)
were studied through half diallel analysis of 28 F1 hybrids derived by crossing 8 parental
lines. The study indicated the preponderance of non-additive gene action for days to 50%
flowering, nodes per plant, fruit length, fruit diameter, plant height, fruits per plant and
mucilage and a preponderance of additive gene action for days to first picking, first fruit
producing node, internodal length, average fruit weight and harvest duration. For fruit
yield per plant and dry matter, only dominant component of variance was observed which
revealed the presence of non-additive gene action, hence, heterosis breeding is required to
be followed for exploitation of thesetraits.

40. The study was carried out to determine the type of gene action, genetic parameters of yield
and other quantitative traits by crossing 8 diverse maize inbred lines in complete diallel
fashion. Seed of F1 population along with their parents was planted in randomized complete
block design replicated thrice. The estimates of components of genetic variation revealed
that non additive genetic effects were more pronounced in the inheritance of plant height,
days to 50% tasseling, days to 50% silking, ear height and grain yield per plant. Directional
dominance was observed for all the characters under study. The graphic analysis showed
that all the characters were under the genetic control of over dominance type of gene action,
therefore, the material can easily be exploited for heterotic effect.